Screen printing method

ABSTRACT

It is possible to obtain a screen printing method that may assure excellent printing qualities since the screen printing method of the present invention includes: (A) sliding a squeegee head with paste stored in the squeegee head on a mask plate, while the past is pressurized, and printing the paste on a substrate through pattern holes of the mask plate, (B) at least one step of (b) separating the squeegee head with the paste stored therein from the mask plate, and (e) sliding the squeegee head on the mask plate for a pre-squeezing purpose before the step (A). The step of separating the squeegee head from the mask plate includes the steps of (1) discontinuing the pressure application to the paste stored in the squeegee head, (2) horizontally moving the squeegee head by a predetermined distance while the bottom end portion of the squeegee head is abutted on the mask plate in a state of the pressure application being discontinued, and (3) moving the squeegee head upward off from the mask plate. In the step of pre-squeezing includes the steps of (1) pressurizing the paste stored in the squeegee head in a state of the squeegee head being abutted on the mask plate, and (2) horizontally moving the squeegee head while the bottom end portion of the squeegee head is abutted on the mask plate in a state of the paste being pressurized.

FIELD OF THE INVENTION

The present invention relates to a screen printing method for printingcream solder, conductive paste or like paste on a substrate.

BACKGROUND OF THE INVENTION

Conventionally, screen printing has been adopted for printing creamsolder, conductive paste or like paste on substrates in a process ofmounting electronic components on a substrate. This method comprises aprocess of setting a mask plate with pattern holes provided thereinaccording to the printing portions and a process of printing paste on asubstrate by squeezing through the pattern holes of the mask plate.

As a squeezing method for such screen printing, a method using a closedtype squeegee head is known. In this method, a squeegee head providedwith a paste storage container having an opening at the bottom thereofis used. With the opening abutted on the mask plate, the paste in thepaste storage container is pressurized so that the paste is pushed andfilled into the pattern holes of the mask plate through the opening.And, the squeegee head is slid on the mask plate, then the paste isfilled into each pattern hole in order.

In such a conventional screen, printing method using a closed typesqueegee head, there are problems as described in the following. In thescreen printing operation, the squeegee head is in a state such that thebottom opening thereof is always contacted on the surface of the maskplate. However, it is necessary to separate the squeegee head from thescreen mask, for example, when making the arrangements for the purposeof type change and carrying out the maintenance of the apparatus.

In this case, the paste is always in contact with the mask plate via thebottom opening at the closed type squeegee head. Accordingly, when thesqueegee head moves upward, some of the paste in the squeegee head isliable to remain sticking to the surface of the mask plate. And, in casethere remains some paste on the mask plate, it is necessary to wipe offthe paste sticking to the mask plate. Therefore, in the conventionalmethod, there is a problem of such residual paste that is discardedwastefully. Moreover, it is necessary to wipe off each time the pastesticking to the mask plate, and consequently, there has been a problemof a loss of time required for the arrangements and maintenance.

On the other hand, cream solder or the like paste used for screenprinting contains resin component. The resin component easily shows ahardening reaction. In order to prevent such hardening reaction of thepaste, the paste is kept at a constant temperature in a refrigerator orthe like until the paste is used. And, when the paste is used, it istimely taken out of the refrigerator, taking into account thepredetermined time of leaving the paste in the atmosphere, and then thepaste is placed into the squeegee head.

The viscosity of such paste will vary depending upon the ambientatmospheric conditions, and further, the viscosity is liable to changewith the lapse of time. For example, (a) at the time when the paste istaken out of the refrigerator and placed in the printing apparatus, and(b) after starting to use the paste, when-the paste has been left in theapparatus for a long time while the printing operation is discontinued,then suitable viscosity for printing cannot be obtained. Thus, when theviscosity of the past used for screen printing is not appropriate, it isimpossible to obtain reliable printing qualities.

The present invention is intended to provide a screen printing methodthat may assure reliable printing qualities.

SUMMARY OF THE INVENTION

The screen printing method of the present invention comprises:

(A) a step of sliding a squeegee head with paste stored in the squeegeehead on a mask plate while the paste is pressurized, and printing thepaste on a substrate through a pattern hole of the mask plate;

(B) at least one step of (b) separating the squeegee head with the pastestored in the squeegee head from the mask plate; and

(e) pre-squeezing the squeegee head on the mask plate before the step(A).

The step of separating the squeegee head from the mask plate comprises:

(1) a step of discontinuing the pressure application to the paste storedin the squeegee head;

(2) a step of horizontally moving the squeegee head by a predetermineddistance while the bottom end portion of the squeegee head is abutted onthe mask plate in a state of the pressure application beingdiscontinued; and

(3) a step of moving the squeegee head upward off from the mask plate.

The step of pre-squeezing comprises:

(1) a step of pressurizing the paste stored in the squeegee head in astate of the squeegee head being abutted on the mask plate; and

(2) a step of horizontally moving the squeegee head while the bottom endportion of the squeegee head is abutted on the mask plate in a state ofthe paste being pressurized.

With the configuration, it is possible to assure reliable printingqualities.

Further, by the screen printing method comprising the (b) step, it isable to reduce the quantity of paste discarded wastefully without beingused for printing, in addition to the advantage described above. Also,it is possible to avoid carrying out extra work for arrangements andmaintenance.

At the other time, the screen printing method comprising the (e) step,it is able to lower the viscosity of paste making it appropriate forscreen printing, thereby further improving the printing qualities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a screen printing apparatus in an embodimentof the present invention.

FIG. 2 is a side view of a screen printing apparatus in an embodiment ofthe present invention.

FIG. 3 is a fragmentary sectional view of a squeegee head of a screenprinting apparatus in an embodiment of the present invention.

FIGS. 4a-4 e are explanatory diagrams of processes based on a screenprinting method in an embodiment of the present invention.

FIGS. 5a-5 d are explanatory diagrams of processes based on a screenprinting method in another embodiment of the present invention.

DESCRIPTION OF REFERENCE NUMERALS

1 Positioning section

2 Substrate holder

3 Substrate

4 Clamper

5 Paste, cream solder

10 Screen mask

11 Holder

12 Mask plate

12 a Pattern hole

13 Squeegee head

14 Printing section

15 Connection member

16 Cylinder

16 a Rod

20 Head hoisting unit

21 Plate member

22 Cylinder

23 Slider

24 Guide rail

25 Frame

26 Nut

27 Feed screw

28 Motor

30 Main body

31 Cartridge

31 a Push-out plate

31 b Opening

32 Pressure plate

34 Throttle plate

34 a Opening

35 Printing space

36A Scraping member

36B Scraping member

DETAILED DESCRIPTION OF THE INVENTION

A screen printing method in one embodiment of the present invention is amethod for printing paste on a substrate through pattern holes of a maskplate by pressurizing the paste while sliding a squeegee head with thepaste stored therein on the mask plate. The printing method comprises astep of separating the squeegee head from the mask plate.

The step of separating the squeegee head from the mask plate includes:

(a) a step of discontinuing the pressure application to the paste storedin the squeegee head when separating the squeegee head from the maskplate;

(b) a step of horizontally moving the squeegee head by a predetermineddistance while the bottom end thereof is abutted on the mask plate in astate of the pressure application being discontinued; and

(c) a step of moving the squeegee head upward off from the mask plate.In this way, the squeegee head is separated from the mask plate.

With this configuration, it is possible to realize a screen printingmethod that may assure excellent printing qualities. Further, thesqueegee head can be separated from the mask plate while the paste isless in adhesion on the mask plate surface. As a result, it is possibleto prevent the paste from sticking to the mask plate surface andremaining thereon.

Preferably, in a step of horizontally moving the squeegee head by apredetermined distance while the bottom end portion of the squeegee headis abutted on the mask plate in a state of the pressure applicationbeing discontinued, the paste sticking to the mask plate comes off themask plate, and thus, the paste becomes released from the mask plate.

Preferably, the printing method further comprises

(c) a step of changing the type of the substrate in a state of thesqueegee head being separated from the mask plate.

Preferably, the printing method further comprises

(c) a step of feeding the paste into the squeegee head in a state of thesqueegee head being separated from the mask plate.

Preferably, the step of horizontally moving the squeegee head includes astep of horizontally moving the squeegee head in a state of a damper ofa substrate holder being abutted on the bottom surface of the maskplate.

Preferably, after horizontal movement of the squeegee head, the squeegeehead starts moving upward off from the mask plate.

Preferably, while the squeegee head is moving horizontally, the squeegeehead starts moving upward off from the mask plate.

Preferably, a part of the mask plate is held on the damper which servesto hold the mask plate, the substrate is placed under the other part ofthe mask plate, and within the range of the position where the maskplate is held on the clamper, the squeegee head horizontally moves whileabutting on the mask plate.

Preferably, the paste is air-tightly stored in the squeegee head, andwhen the squeegee head is in contact with the surface of the mask plate,the paste is air-tightly existing in a printing space surrounded by thesqueegee head and the mask plate.

A screen printing method in another embodiment of the present inventionis a method for printing paste on a substrate through pattern holes of amask plate by pressurizing the paste while sliding a squeegee head withpaste stored therein on the mask plate, the screen printing methodcomprises

(a) a step of pressurizing the paste stored in the squeegee head whichis abutted on the mask plate before starting the screen printingoperation; and

(b) a step of reciprocally moving the squeegee head in the horizontaldirection while the bottom end portion of the squeegee head is abuttedon the mask plate in a state of the paste being pressurized. In thisway, the step of pre-squeezing is performed.

With this configuration, it is possible to obtain a screen printingmethod that may assure excellent printing qualities. The paste isstabilized at the predetermined viscosity that is suitable for printing.As a result, the printing qualities will be further improved.

Preferably, a step of horizontally moving the squeegee head includes astep of reciprocally moving the squeegee head in the horizontaldirection.

Preferably, the paste pushed out into the printing space of the squeegeehead is given a rolling motion during the step of pre-squeezingoperation, and the paste is lowered in viscosity due to the rollingmotion.

Preferably, the paste stored in the squeegee head is given a rollingmotion during the step of the pre-squeezing operation, and the paste islowered in viscosity due to the rolling motion.

Preferably, the printing method further comprises

(f) a step of feeding the paste into the squeegee head, wherein the stepof the pre-squeezing operation is performed between the step of feedingthe paste into the squeegee head and the step of printing the paste onthe substrate.

Preferably, the printing method further comprises

(g) a step of discontinuing printing operation, wherein the step of thepre-squeezing operation is performed between the step of discontinuingthe printing operation and the step of printing the paste on thesubstrate.

Preferably, the step of horizontally moving the squeegee head while thebottom end portion thereof is abutted on the mask plate in a state ofthe squeegee head being in contact with the mask plate includes a stepof abutting a damper against the bottom surface of the mask plate whilethe substrate holder is moved upward.

Preferably, a part of the mask plate is held on the damper which servesto hold the mask plate; the substrate is placed under the other part ofthe mask plate; and within the range of the position where the maskplate is held on the clamper, the squeegee head horizontally moves whileabutting on the mask plate.

Preferably, the step of horizontally moving the squeegee head in thestep of the pre-squeezing operation includes a step of reciprocalmovement at a constant speed.

Preferably, the step of horizontally moving the squeegee head in thestep of the pre-squeezing operation includes at least one of

(i) a movement of increasing the speed gradually from a low speed to ahigh speed; and

(ii) a movement of repeating a pattern of speed change from low to highspeed by a plurality of times.

Preferably, the paste is air-tightly stored in the squeegee heat, andwhen the squeegee head is in contact with the surface of the mask plate,the paste is given a rolling motion in a printing space surrounded bythe squeegee head and the mask plate.

Cream solder, conductive paste and the like paste may be used as thepaste material.

A screen printing method in an exemplary embodiment of the presentinvention will be described in the following with reference to thedrawings.

Exemplary Embodiment 1

FIG. 1 is a front view of a screen printing apparatus in an exemplaryembodiment of the present invention. FIG. 2 is a side view of a screenprinting apparatus in an exemplary embodiment of the present invention.FIG. 3 is a fragmentary sectional view of a squeegee head of a screenprinting apparatus in an exemplary embodiment of the present invention.FIG. 4 is an explanatory diagrams of processes based on a screenprinting method in an exemplary embodiment of the present invention.

First, the structure of the screen printing apparatus will be describedwith reference to FIG. 1 and FIG. 2.

In FIG. 1 and FIG. 2, a substrate positioning section 1 includes asubstrate holder 2 disposed on a movable table (not shown). Thesubstrate holder 2 includes a damper 4. A substrate 3 subjected toscreen printing is held by the damper 4. By driving the movable table,the substrate 3 held by the substrate holder 2 may be positioned inhorizontal and vertical directions.

A screen mask 10 is disposed above the positioning section 1. The screenmask 10 includes a holder 11 and a mask plate 12 held by the holder 11.Pattern holes 12 a are made in the mask plate 12, corresponding to theprinting portions of the substrate 3 subjected to mask printing.

A squeegee head 13 is disposed on the screen mask 10 by means of a headhoisting unit 20 in a manner such that the squeegee head 13 is free tomove up and down. The head hoisting unit 20 includes a cylinder 22vertically disposed on a plate member 21. The squeegee head 13 isconnected to the bottom end portion of a rod 22 a of the cylinder 22 viaa connection member 15. By driving the cylinder 22, the squeegee head 13may be moved up and down against the mask plate 12. The squeegee head 13is moved up and down against the screen mask 10. That is, the headhoisting unit 20 has a function as a means to move the squeegee head 13up and down.

A slider 23 is fixed to each bottom end portion of the plate member 21of the head hoisting unit 20. A guide rail 24 is disposed on the uppersurface of a frame 25. The slider 23 is slidably fitted in the guiderail 24. A nut 26 is attached to the bottom of the plate member 21. Afeed screw 27 screwed in the nut 26 is driven and turned by a motor 28.

When the motor 28 is driven, the plate member 21 moves horizontally, andthe squeegee head 13 connected to the head hoisting unit 20 also moveshorizontally. With the squeegee head 13 shifted down, when the motor 28is operated, the squeegee head 13 moves horizontally on the mask plate12. That is, the motor 28, the feed screw 27 and the nut 26 serve tohorizontally move the squeegee head 13 on the mask plate 12. The motor28, feed screw 27 and nut 26 serve a function as a moving means.

Cream solder 5 is used as the paste. A printing section 14 is providedat the bottom of the squeegee head 13. The printing section 14 abuts onthe surface of the mask plate 12, and the cream solder 5 is filled intopattern hole 12 a.

The printing section 14 will be described with reference to FIG. 3.

In FIG. 3, main body 30, having a block member, is long and narrow inshape along the widthwise direction of the mask plate 12. As shown inFIG. 2, the length of the main body 30 is set so as to cover the widthof substrate 3. Recess 30 a is formed in the main body 30. A cartridge31 is removably mounted in the recess 30 a. The cream solder 5 is storedin the cartridge 31.

The cartridge 31 has a function as a storage section (paste storagesection) to store cream solder. A predetermined quantity of cream solderis previously stored in the cartridge 31. The cartridge 31 containingcream solder is mounted in the main body 30 when printing is started. Apressure plate 32 for pressurizing the cream solder 5 in the cartridgeis fitted in the upper opening of the cartridge 31. The pressure plate32 is connected to rod 16 a of cylinder 16 arranged above the pressureplate 32. When the cylinder 16 is driven, the pressure plate 32 moves upand down in the cartridge 31.

Also, the bottom surface of the cartridge 31 serves a function as apush-out plate 31 a for cream solder. The push-out plate 31 a hasmultiple openings 31 b. When the pressure plate 32 is pressed down bythe cylinder 16, the cream solder 5 in the cartridge 31 is pressurizedand pushed out through the openings 31 b of the push-out plate 31 a. Thecylinder 16 and the pressure plate 32 serve a function as a pressuremeans for pressurizing the cream solder 5.

A throttle plate 34 is disposed at the bottom of main body 30. Thethrottle plate 34 also has multiple openings 34 a the same as thepush-out plate 31 a of the cartridge 31. When cream solder 5 is pushedout by the cylinder 16, the cream solder 5 moves downward passingthrough the openings 31 b of push-out plate 31 a and the openings 34 aof throttle plate 34. Then, the pushed out cream solder 5 reaches aprinting space 35 formed beneath the main body 30. The printing space 35is surrounded by two scraping members 36A, 36B disposed inwardlyslantwise under the main body 30 and the bottom surface of the main body30

The scraping members 36A, 36B respectively form a front wall and a rearwall in the squeezing direction of the printing space 35. With thesqueegee head 13 shifted down, the bottom ends of the scraping members36A, 36B are abutted on the surface of the mask plate 12. In theprinting operation, the printing space 35 accommodates the pressurizedcream solder 5, and the cream solder 5 comes in contact with the surfaceof the mask plate 12 through the opening between the scraping member 36Aand scraping member 36B.

When the pressure plate 32 is pressed down, the cream solder 5 in thecartridge 31 is pressurized. Consequently, the cream solder 5 moves intothe printing space 35, passing through the push-out plate 31 a and thethrottle plate 34. There are area-reduced portions in the passage ofcream solder 5. The area-reduced portions include many small openings 31b and 34 a by which the sectional area of the solder passage is reduced.When the pressurized cream solder 5 passes through the area-reducedportions, the cream solder 5 decreases in viscosity and is improved inproperty to become suitable for screen printing. In this way, the creamsolder 5 improved in viscosity is filled into the printing space 35.

In screen printing, with the printing space 35 filled with cream solder5, the squeegee head 13 moves sliding on the mask plate 12. Thus, thecream solder 5 in the printing space 35 goes through the opening formedbetween the scraping members 36A, 36B and is filled into the patternholes 12 a of the mask plate 12.

And, as the squeegee head 13 moves, the cream solder 5 is filled intothe pattern holes 12 a in order. When all pattern holes 12 a have beenfilled with cream solder 5, substrate holder 2 is moved down, separatingthe substrate from the mask plate 12. That is, the cream solder 5 in thepattern holes 12 a moves downward along with the substrate 3, coming offof the pattern holes 12 a, and thereby, the cream solder 5 is printed onthe substrate 3. Thus, the screen printing operation is completed.

Next, a squeegee head separating operation in cream solder printing willbe described with reference to FIG. 4. The squeegee head separatingoperation is performed when making arrangements for type change ofsubstrate 3, feeding cream solder 5 into squeegee head 13, or performingmaintenance of the apparatus. In this operation, the squeegee head 13 ismoved upward off from mask plate 12.

In FIG. 4(a), while cream solder 5 in cartridge 31 is pressurized bypressure plate 32, squeegee head 13 is horizontally moved on mask plate12, thereby finishing one cycle of printing operation. FIG. 4(a) shows astate with one cycle of printing operation competed. In this state ofoperation, substrate holder 2 is shifted down, and lamper 4 is in aposition apart from the bottom of mask plate 12.

Next, as shown in FIG. 4(b), pressure plate 32 moves up to discontinuepressurizing cream solder 5. Then, the pressure of cream solder 5 inprinting space 35 is released from the surface of mask plate 12.

After that, as shown in FIG. 4(c), substrate holder 2 moves up and oneclampers 4 is abutted on the bottom surface of mask plate 12 just undersqueegee head 13.

In this state of operation, motor 28 is operated, and as shown in FIG.4(d), the squeegee head 13 horizontally moves on the mask plate 12 beingsupported on the upper surface of clamper 4. It is possible tohorizontally move the squeegee head 13 in an optional position on themask plate 12. Preferably, the squeegee head 13 is horizontally moved onthe mask plate 12 being stably supported, for example, on the surface ofclamper 4.

As the squeegee head 13 moves horizontally, cream solder 5 being intight contact with the upper surface of mask plate 12 through theopening of printing space 35 moves sliding on the mask plate 12. In thisway, the cream solder 5 sticking to the mask plate 12 comes off andreleased therefrom, greatly decreasing in adhesion.

And then, as shown in FIG. 4(e), cylinder 22 is driven to move squeegeehead 13 upward. During this upward operation, in a state with theadhesion of cream solder 5 on mask plate 12 decreased, the bottom endsof scraping plates 36A, 36B come off from the mask plate 12.

By this method, the cream solder 5 in the printing space 35 may beprevented from sticking to the mask plate 12 and remaining thereon.

And it is possible to start the upward operation after completion ofhorizontal movement of the squeegee head 13. Also, it is possible tostart the upward operation while moving the squeegee head 13horizontally.

Accordingly, it is not necessary to remove the cream solder 5 remainingon the mask plate 12 as is required in the prior art when moving up theclosed type squeegee head 13. Thus, wasteful work may be eliminated andit is possible to avoid the loss of time for arrangements andmaintenance. Further, the quantity of cream solder discarded withoutbeing used for printing will be reduced, enhancing the effective use ofresources. Also, since no cream solder unnecessarily remains on the maskplate, the printing accuracy is improved, resulting in improvement ofthe printing qualities.

Exemplary Embodiment 2

A screen printing method in another exemplary embodiment of the presentinvention will be described in the following with reference to FIG. 5.The screen printing apparatus shown in FIG. 1, FIG. 2 and FIG. 3 asdescribed in the above exemplary embodiment 1 is used in this exemplaryembodiment.

The description is given to the pre-squeezing operation in the method ofprinting cream solder 5 by squeegee head 13. The pre-squeezing operationis performed to make the viscosity of cream solder 5 appropriate forprinting operation after feeding cream solder 5 into the squeegee heador during interruption of screen printing operation waiting for the nextprocess.

First, in FIG. 5(a), squeegee head 13 moves down to mask plate 12, andthe bottom end of same abuts on the mask plate 12. Then, substrateholder 2 moves upward, and clamper 4 is pressed against the bottomsurface of the squeegee head 13 via the bottom surface of the mask plate12. In this state of operation, pressure plate 32 moves down topressurize cream solder 5 in the squeegee head 13.

Next, as shown in FIG. 5(b), motor 28 is driven, and then the squeegeehead 13 horizontally moves to the right on the mask plate 12 within arange such that the bottom end abutting the mask plate 12 does not gobeyond the range of clamper 4.

Subsequently, as shown in FIG. 5(c), the squeegee head 13 horizontallymoves in the opposite direction. Further, as shown in FIG. 5(d), thesqueegee head 13 horizontally moves again to the right. Such reciprocalmovement of the squeegee head 13 is repeated by the predetermined numberof times.

Due to the reciprocal movement of the squeegee head 13, the cream solder5 filled in printing space 35 is given a rolling motion. And rolling ofthe cream solder 5 in the printing space 35 causes the cream solder 5 tobe lowered in viscosity, and consequently, the cream solder 5 will beimproved in fluidity. Generally, when the cream solder 5 is left at astandstill for many hours, the cream solder will increase in viscosityand become inappropriate for screen printing. On the other hand,pre-squeezing operation on cream solder 5 as described may decrease theviscosity of the cream solder 5. That is, “kneading” of cream solder 5is effective to decrease the viscosity of the cream solder 5, and thecream solder 5 is then improved in quality and becomes suitable forscreen printing. The screen printing operation is started aftercompletion of such predetermined pre-squeezing operation. As a result,the printing accuracy and printing qualities may be improved.Incidentally, the word “viscosity” used in the above description may bereplaced by “kinematic viscosity.”

Preferably, the moving speed of the squeegee head 13 in thepre-squeezing operation is kept constant. Also, the moving speed of thesqueegee head 13 gradually increases from a high speed to a low speed.Also, the squeegee head 13 repeats a pattern of speed change from low tohigh speed by a plurality of times. In this way, the squeegee head 13changes its moving pattern to perform appropriate pre-squeezingoperation in accordance with the properties and characteristics of thecream solder 5. Also, it is possible to reciprocally move the squeegeehead 13 in an optional position on the mask plate 12. Preferably, thesqueegee head 13 is moved in a state such that the mask plate 12 isstably supported by damper 4 or the like. The squeegee head 13 is ableto make a one-way movement instead of a reciprocal movement. However,the squeegee head 13 is preferable to make a reciprocal movement inorder to further enhance the above-mentioned advantage.

Since the structure of the squeegee head 13 is of closed type, even incase of setting the moving pattern of squeegee head 13 to variouspatterns with high speeds and low speeds combined as described above forthe purpose of effectively performing the pr-squeezing operation, thecream solder 5 to be kneaded is closed in a space between the printingspace of squeegee head 13 and the mask plate. Therefore, the creamsolder 5 may be prevented from spattering during the pre-squeezingoperation. Accordingly, it is possible to freely set the pattern ofpre-squeezing operation in accordance with the printing object. Also, itis possible to efficiently perform the pre-squeezing operation. As aresult, the printing qualities may be improved.

Exemplary Embodiment 3

A screen printing method in this exemplary embodiment comprises both ofthe screen printing method described in the exemplary embodiment I andthe screen printing method described in the exemplary embodiment 2.

That is, the screen printing method comprises

(a) a step of pressurizing paste while sliding a squeegee head with thepaste stored therein on a mask plate and printing the paste on asubstrate through pattern holes of the mask plate,

(b) a step of separating the squeegee head with the paste stored in thesqueegee head from the mask plate, and

(e) a step of pre-squeezing operation by moving the squeegee head on themask plate to perform squeezing of the paste before the step (a).

The step of separating the squeegee head from the mask plate includes

(1) a step of discontinuing the pressure application to the paste storedin the squeegee head,

(2) a step of horizontally moving the squeegee head by a predetermineddistance while the bottom end portion of the squeegee head is abutted onthe mask plate in a state of the pressure application beingdiscontinued, and

(3) a step of moving the squeegee head upward off from the mask plate.

The step of the pre-squeezing operation includes

(i) a step of pressurizing the paste stored in the squeegee head whilethe squeegee head is abutted on the mask plate, and

(ii) a step of horizontally moving the squeegee head while the bottomend portion of the squeegee head is abutted on the mask plate in a stateof the paste being pressurized.

The detail of the present exemplary embodiment is the same as for theexemplary embodiment 1 and the exemplary embodiment 2.

With this configuration, the quantity of paste discarded without beingused for printing will be reduced. Further, it is possible to avoidwasteful work for arrangements and maintenance, and also, to assurereliable printing qualities.

As described above, the present invention includes a step ofdiscontinuing pressure application to internally stored paste when asqueegee is separated from a mask plate, a step of horizontally movingthe squeegee head by a predetermined distance while the squeegee head isabutted on the mask plate in a state of the pressure application beingdiscontinued, and a step of separating the squeegee head from the maskplate while the adhesion between the paste and the mask plate surface isdecreased, and thereby, it is possible to prevent the paste fromremaining on the mask plate surface. Accordingly, it is not necessary tocarry out work to remove paste remaining on the mask plate. Thus, thetime otherwise required for such extra work can be saved. Further, it ispossible to reduce the quantity of paste discarded without being usedfor printing, thereby enhancing the effective use of resources.

Also, the internally stored paste is pressurized while the squeegee headis abutted on the mask plate, and the squeegee head abutted on the maskplate is reciprocally moved in the horizontal direction to performpre-squeezing operation prior to start of the screen printing operation.Accordingly, the viscosity of the paste will be stabilized and, as aresult, it is possible to assure excellent printing qualities.

What is claimed is:
 1. A screen printing method, comprising: (A) a stepof sliding a squeegee head with paste stored in the squeegee head on amask plate, while said paste is pressurized, and printing said paste ona substrate through a pattern hole of said mask plate, and (B)separating said squeegee head with said paste stored therein from saidmask plate, wherein said step of separating said squeegee head from saidmask plate comprises the steps of: (1) discontinuing pressureapplication to said paste stored in said squeegee head, (2) horizontallymoving said squeegee head by a predetermined distance while the bottomend portion of said squeegee head is abutted on said mask plate in astate of the pressure application being discontinued, and (3) movingsaid squeegee head upward off from said mask plate, and wherein, in thestep of horizontally moving said squeegee head by a predetermineddistance while the bottom end portion of said squeegee head is abuttedon said mask plate in a state of said pressure application beingdiscontinued, said paste sticking to said mask plate comes off said maskplate, and said paste becomes released from said mask plate, due to astep of pre-squeezing said squeegee head on said mask plate before saidstep (A) said paste pushed out into a printing space of said squeegeehead is given a rolling motion, and the rolling motion of said pastecauses said paste to be lowered in viscosity.
 2. The screen printingmethod of claim 1, wherein said paste is air-tightly stored in saidsqueegee head, and when said squeegee head is in contact with thesurface of said mask plate, said paste is air-tightly existing in aprinting space surrounded by said squeegee head and said mask plate. 3.A screen printing method comprising the steps of: (a) sliding a squeegeehead with paste stored in the squeegee head on a mask plate, while saidpaste is pressurized, and printing said paste on a substrate through apattern hole of said mask plate, and (b) separating said squeegee headwith said paste stored therein from said mask plate, wherein the step ofseparating said squeegee head from said mask plate comprising the stepsof (1) discontinuing pressure application to said paste stored in saidsqueegee head, (2) horizontally moving said squeegee head by apredetermined distance while the bottom end portion of said squeegeehead is abutted on said mask plate in a state of the pressureapplication being discontinued, and (3) moving said squeegee head upwardoff from said mask plate.
 4. The screen printing method of claim 3,wherein, in the step of horizontally moving said squeegee head by apredetermined distance while the bottom end portion of said squeegeehead is abutted on said mask plate in a state of said pressureapplication being discontinued, said paste sticking to said mask platecomes off said mask plate, and said paste becomes released from saidmask plate.
 5. The screen printing method of claim 3, further comprisingthe step of (c) changing the type of said substrate in a state of saidsqueegee head being separated from said mask plate.
 6. The screenprinting method of claim 3, further comprising the step of (d) feedingfurther paste into said squeegee head in a state of said squeegee headbeing separated from said mask plate.
 7. The screen printing method ofclaim 3, wherein the step of horizontally moving said squeegee headincludes a step of horizontally moving said squeegee head in a state ofa clamper of a substrate holder being abutted on the bottom end surfaceof said mask plate.
 8. The screen printing method of claim 3, whereinsaid squeegee head starts to move upward off from said mask plate afterhorizontal movement of said squeegee head.
 9. The screen printing methodof claim 3, wherein said squeegee head starts to move upward off fromsaid mask plate while said squeegee head is horizontally moving.
 10. Thescreen printing method of claim 3, wherein a part of said mask plate isheld on a clamper which serves to hold said mask plate, said substrateis placed beneath the other part of said mask plate, and within therange of the position where said mask plate is held on said clamper,said squeegee head horizontally moves while abutting on said mask plate.11. The screen printing method of claim 3, wherein said paste is creamsolder.
 12. The screen printing method of claim 3, wherein said paste isair-tightly stored in said squeegee head, and when said squeegee head isin contact with said mask plate, said paste is air-tightly existing in aprinting space surrounded by said squeegee head and said mask plate. 13.The screen printing method of claim 3, further comprising the step of(e) pre-squeezing operation of said squeegee head on said mask platebefore the step (a), wherein said step of pre-squeezing comprises thesteps of (i) pressurizing paste stored in said squeegee head in a stateof said squeegee head being abutted on said mask plate, and (ii)horizontally moving said squeegee head while the bottom end portion ofsaid squeegee head is abutted on said mask plate in a state of saidpaste being pressurized.